Implant with antimicrobial coating

ABSTRACT

In a coated implant that releases silver ions in the human body and thereby has an antimicrobial effect, a first surface component of the coating is formed by an anode material. A second surface component of the coating is formed by a cathode material. The cathode material is higher in the electrochemical voltage sequence than the anode material. The cathode and the anode are connected with one another in an electrically conducting manner. Together with the body electrolyte in the vicinity of the implant the anode and the cathode material form a plurality of local galvanic elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of EP Application No. 10004140.9 filed 19 Apr. 2010; and U.S. Provisional Application Ser. No. 61/424,270 filed 17 Dec. 2010; which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The invention relates to an implant with a coating that releases silver ions in the human body and results in an antimicrobial effect

BACKGROUND

When implants are inserted into the human body, there is a risk of infections. Triggers for infections can be microorganisms that are brought into the human body or that are located on the surface of the implant. It is known that the risk of infections can be diminished by providing the implant with a coating that releases silver ions into their vicinity. The silver ions have a known antimicrobial effect. In addition they have the advantage that—if they do not encounter a microorganisms and act against it—they combine with the chloride of the body electrolyte to AgCl and can be excreted from the body in this form. In contrast to other antimicrobially effective materials the silver ions do therefore not accumulate in the body.

The known silver coatings release silver ions only to a limited extent The released silver ions in addition move only incidentally in the vicinity of the implant. There is therefore a high probability that the silver ions combine in the body electrolyte to form AgCl and thereby lose their antimicrobial effectiveness before they encounter a microorganism.

SUMMARY

The present disclosure provides an implant whose coating features an improved antimicrobial effectiveness. Advantageous embodiments are described herein.

According to one embodiment a first surface component of the coating is formed by a silver-containing anode material that is provided for the release of silver ions. For a second surface component a cathode material is provided. The cathode material is higher in the electrochemical voltage sequence than the anode material. The cathode material and the anode material are connected with one another in an electrically conducting manner.

Initially a few terms are explained. The term implant encompasses all types of objects that are inserted into the body. These include, for example, endoprotheses for bones or joints, but also implants that are inserted into other parts of body tissue, such as, for example, stents in the heart circulatory system. Encompassed also are implants that are only partially inserted into the human body and protrude in part, such as tooth implants or external fixators that represent an indirect osteosynthesis external to the body that is partially stabilized with a tensioning device.

The terms first surface component and second surface component express that the cathode material in the coating is spatially separated from the anode material. Not meant by this is a coating in which several materials are evenly mixed with one another. It is possible but not strictly required that the second surface component is covered comprehensively with the cathode material.

In the electrochemical voltage sequence the materials are sorted according to their standard electrode potential. The higher the position of a material in the electrochemical voltage sequence the lower is its release pressure, meaning its tendency to release ions into the water present in the vicinity. A metal that is positioned higher in the electrochemical voltage sequence is labeled as precious; a metal that is positioned lower in the electrochemical voltage sequence, is labeled as base. For most materials the position in the electrochemical voltage sequence is known, the respective value can be obtained from the relevant tables. If the position of a material in the electrochemical voltage sequence is not known, it can be determined by means of building a galvanic element with a known material and measuring the generated potential difference. Based on the potential difference the position in the voltage sequence can be determined. The terms anode material and cathode material serve the purpose of representing the relative position of the utilized materials relative to one another in the electrochemical voltage sequence. The cathode material and the anode material are electrically conducting materials.

When the implant is inserted into the body, the anode material and the cathode material of the coating form with the body electrolyte in the vicinity of the implant a local galvanic element. The tendency of the anode material to release silver ions into the vicinity is thereby amplified. The electrons that remain behind after the release of the silver ions in the anode material can move into the cathode material because of the electric connection. Because of the potential difference the silver ions are attracted in the direction of the cathode material.

The effect of the coating according to the invention is therefore doubled. First, the anode material has, because of the local galvanic element an increased tendency to releast silver ions into the surrounding body electrolyte. Compared with a coating that consists only of the respective anode material, a larger number of silver ions is therefore released, with the result that the antimicrobial efficacy is increased. Furthermore the movement of the released silver ions is no longer in any arbitrary direction, but the silver ions are moved in the direction of the potential difference between the two materials, meaning in the direction of the cathode material. The probability is increased that the silver ions will in fact become effective against the microorganisms that are situated on the surface of the implant instead of combining in the body electrolyte to AgCl and losing thereby the antimicrobial efficacy. The effect of the coating according to the invention is therefore concentrated on the surface of the implant. The coating is particularly suited for fighting the dangerous biofilm that can form on the surface of implants.

The coating can cover the entire surface of the implant. This will be desirable in the context of many implants that are entirely inserted into the body. In particular in the case of joint prostheses it can also be provided that only one part of the surface is coated. The coating can be deposited on the part of the surface with which the prosthesis, in the implanted state, is in contact with bodily tissue, while another part of the surface, which for example is intended for the interaction with another prosthesis components or, as in the case of the fixator, is located external to the body, is free of the coating.

The anode material can be made of pure silver, or any percentage thereof, including, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9%. With a standard electrode potential of about +0.8 V, silver is a relatively precious metal that belongs in the upper range of the electrochemical voltage sequence. A reference size for the voltage specifications of the standard electrode potential is the normal hydrogen electrode.

The cathode material that acts together with the pure silver has to have a standard electrode potential of more than +0.8 V. If the cathode material is a metal, it is therefore more precious than silver. A cathode material suitable for the interaction with pure silver is for example gold, which features a standard electrode potential on the order of +1.5 V. Even if not pure silver but an alloy of silver and another material is utilized as anode material, the standard electrode potential of the cathode material should be larger than about +0.8 V. Preferably the standard electrode potential of the cathode material is greater by at least about 0.3 V, by at least about 0.5 V, or by at least about 0.7 V than the standard electrode potential of the anode material.

The larger the difference between the standard electrode potential of the anode material and the standard electrode potential of the cathode material, the stronger the effect of the local galvanic element. In an advantageous embodiment form a silver-containing material is therefore utilized as the anode material since its standard electrode potential is smaller than +0.8 V. The anode material in that case comprises, in addition to the silver components, other components that can be released from the anode. The standard electrode potential indicated for the anode material refers to the release pressure for silver ions. Preferably a material is selected for the anode from which no other materials besides the silver ions are released to the body electrolyte. If in addition to the silver ions, other materials are released, the risk exists that the additional materials could have undesirable effects in the body. Therefore, for the anode as well as also for the cathode a material should be chosen that is biocompatible.

The antimicrobial effect of the coating according to the invention depends on the silver ions that are released from the cathode material. As the number of released silver ions increases the greater the surface component of the coating occupied by the anode material. The surface component of the coating that is occupied by the anode material is, therefore, preferably larger than about 50%, larger than about 70%, or larger than about 80% of the total surface area. Comparatively, the area component occupied by the cathode material is of lesser importance. However, the area component of the cathode material must not be too small if a good efficacy of the galvanic elements is be achieved. Preferably the portion of the surface of the coating occupied by the cathode element is larger than about 0.1%, larger than about 1%, or larger than about 5%.

It is desired that the silver ions, after they have exited the anode material, will cover a certain distance before impinging on the cathode material. During this movement the silver ions can act in a antimicrobial manner. The surface components of the coating occupied by the anode material and the cathode material should for this reason be separated from one another in such a manner that the silver ions do not necessarily impinge on the cathode material immediately. The coating encompasses for this reason a plurality of circular surface areas with a diameter preferably of more than about 1 μm, more than about 5 μm, more than about 15 μm, or more than about 50 μm that are formed exclusively from anode material and are free of cathode material. On the other hand, it is not advantageous for the efficacy of the coating if the open path distance over which the silver ions must travel is too long. The diameter of the circular surface areas should for that reason be smaller than about 5 mmm, preferably smaller than about 1 mm, or smaller than about 0.5 mm. Preferably more than about 30%, or more than about 50% of the surface of the coating is occupied by such surface components.

Silver ions exiting in the center of such an area have to cover a certain distance before they impinge on cathode material. While silver ions cover the distance they can act in an antimicrobial manner. The open distance that the silver ions cover can be dimensioned with the diameter of the bacteria in mind, which is also in the pm range. One can assume that the silver ions move along an arch-shaped path and that the largest distance to the surface that the silver ions have along their path is of the same order of magnitude as the distance that is covered parallel to the surface. Therefore, if the covered open path distance corresponds approximately to the diameter of the bacteria, it is accomplished that the silver ions can act against bacteria that are located on the surface during their entire path of travel.

The coating can be designed such that the cathode material is embedded island-shaped in the anode material or is island-shaped deposited on the anode material. The cathode material can itself be deposited in the form of linked surface areas with a diameter of, for example, a few pm. Another possibility is the possibility that the cathode material is deposited on a second surface component in the form of individual particles, without the anode material in this area providing comprehensive coverage.

In many cases the surface of the implant is to be smooth. This can be achieved if the anode material and the cathode material are flush against one another. In an alternative embodiment the cathode material can protrude relative to the anode material. The silver ions then move a small distance to the surface of the coating so that a good effect against microorganisms in the direct vicinity of the coating is achieved. It is desirable to initially deposit the anode material in an even coating thickness and to subsequently deposit cathode material in selected areas on the coating

The coating thickness of the anode materials can be between about 100 nm and about 10,000 nm, preferably between about 200 nm and about 400 nm. This range is particularly valid when the anode material is pure silver. The coating thickness of the cathode material that is deposited on the anode materials can likewise be between about 100 nm and about 10,000 nm, preferably between about 200 nm and about 400 nm.

It is also possible to initially deposit a coating of the cathode material comprehensively. On the cathode material a coating of anode material can be placed that features openings so that the cathode material is accessible through the anode material from the outside. If the anode material is deposited with a plasma coating method, then the openings can be generated due to the fact that during the deposition of the coating larger fragments with a diameter of, for example, 20 μm are aimed at the surface that knock out a piece from the coating that is forming, see WO 2009/036846. With this approach the thickness of the coatings is preferably between about 100 nm and about 10,000 nm, or preferably between about 200 nm and about 400 nm.

One embodiment provides an implant that releases silver ions in the human body and provides an antimicrobial effect, comprising an implant component including a first coating portion forming an anode comprising silver and a second coating portion forming a cathode, wherein the cathode comprises a material having an electrochemical voltage sequence higher than silver, and wherein the cathode and the anode are coupled in an electrically conducting manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by example in what follows in reference to the enclosed drawings using the advantageous embodiment forms. The drawings show:

FIG. 1 shows a first embodiment of an implant;

FIG. 2 shows a component of the implant from FIG. 1;

FIG. 3 shows a second embodiment of an implant;

FIG. 4 shows a section from the body of an implant with coating;

FIG. 5 shows the coating from FIG. 4 in a plan view;

FIG. 6 shows the view from FIG. 4 in the case of a different embodiment;

FIG. 7 shows the view from FIG. 5 in the case of the embodiment according to FIG. 6;

FIG. 8 shows the view from FIG. 4 in the case of a further embodiment; and

FIG. 9 shows the view from FIG. 5 in the case of a further embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An implant shown in FIG. 1 is intended to replace a part of the human skeleton that extends from the hip to below the knee. A sphere-shaped joint head 10 forms a joint surface that is designed to interact with an acetabulum. The joint head 10 is connected with a head piece 11 of the implant by means of a screw connection. The part of the implant that is replacing the center shaft of the femur encompasses three implant components 12, 13, 14. The implant components 12, 13, 14 are also connected among each other and with the head piece 11 by means of screw connections. A knee piece 15 forms an articulated connection with the shaft 16 that is intended to connect the implant with the tibia. The implant components 12, 13, 14 are available in different lengths so that the implant can be adapted to femurs of different length.

FIG. 2 presents an implant component 17 that corresponds to the implant components 12, 13, 14 in an enlarged representation. The implant component 17 encompasses a threaded bolt 18 as well as a threaded bore 19 that is indicated in dashed lines. By means of the threaded bolt 18 and the threaded bore 19 the implant component 17 can be connected at its two ends with other implant components.

The threaded bolt 18, the threaded bore 19 as well as the adjacent front faces 20 and 21, therefore, do not abut, in the implanted state of the implant component 17, against the bodily tissue of the patient, but instead abut against other implant components. The surface area 22 of the implant component 17, on the other hand, is designed for the purpose of being in contact with human tissue in the implanted state. The surface area 22 is provided with an antimicrobial coating 23 that is indicated by means of speckles. The remaining surface of the implant component is free of the coating 23.

The coating 23 is represented in FIGS. 4 and 5 in an enlarged manner. The coating 23 comprises, to a large part, pure silver that coats the surface area comprehensively. Gold in the form of several rectangular islands of cathode material 26 is introduced into the silver coating, as FIG. 5 illustrates. The gold material is embedded in the silver coating so that the two materials abut against each other in a flush manner and a smooth surface is obtained. A smooth surface is desired to minimize irritation of the surrounding bodily tissue as a result of friction. The coating 23 includes a first surface component 28 that is formed by means of the silver material and a second surface component 29 that is formed by means of the gold material. The surface component 28 that is formed by the silver material occupies more than 80% of the surface area formed by the coating 23. Between the islands there remain, as indicated in FIG. 5 in a dashed line, circular surface areas 27 in which the entire surface area formed by the coating 23 comprises silver material and is not interrupted by gold material. The surface area 27 features a diameter of more than 0.1 mm.

The silver and the gold are connected with one another in the coating in an electrically conducting manner. Silver is a less precious metal than gold and is situated lower in the electrochemical voltage sequence than gold. In the sense of the function of the coating according to the invention silver is therefore an anode material 25 and gold is the cathode material 26.

After the implantation, the coating 23 is surrounded with body electrolyte. The silver material has a tendency to release positively charged silver ions into the body electrolyte. This tendency is referred to as release pressure. When silver ions are released out of the coating, excess electrons remain behind in the coating and an excess of negatively charged carriers forms in the coating. Since the silver material and the gold material are connected with one another in an electrically conducting manner, the excess electrons can move freely in the direction of the gold material. The gold material is likewise subject to a certain release pressure to release ions into the body electrolyte. Since gold is a more precious metal than silver and is situated higher in the electrochemical voltage sequence, the release pressure is lower than the release pressure of the silver. The silver ions that are released in larger concentration move toward the gold material. By these means the body electrolyte forms, together with the silver as anode material 25 and with the gold as cathode material 26, local galvanic elements. The silver ions emerge from the anode material 25 and move, parallel to the coating 23, in the direction of the cathode material 26. On this path the silver ions can develop an antimicrobial effect relative to microorganisms that are situated on the surface of the coating 23.

The tooth implant that is shown in FIG. 3 is an alternative embodiment. An implant body 30 is screwed into the jaw bone 31 with its lower end. The upper end of the implant body 30 protrudes from the jaw bone 31 and the gum 32 that surrounds the jaw bone 31 in an upward direction. An abutment post 34 that is covered with an artificial tooth crown 33 is screwed into the open end of the implant body 30. The tooth implant replaces a natural tooth by these means. The implant body 30 in turn is provided with a coating 23 that is indicated by means of speckles.

The coating 23 is represented in FIGS. 6 and 7 in an enlarged manner. On the surface of the implant 30 initially a silver coating is deposited that features an even thickness of about 400 nm. On the surface of the silver coating gold material is deposited in a grid-shaped disposition with a coating thickness of likewise about 400 nm. The areas that are enclosed in the grid, in which the surface of the coating 23 is formed by the silver material, form in their entirety the first surface component 28 of the coating 23. The grid-shaped disposition of the gold material forms the second surface component 29 of the coating. The grid-shape of the gold material is dimensioned in such a manner that circular surface areas 27 with a diameter of more than 50 pm remain free of the gold material.

In the case of the coating shown in FIG. 8 the implant component 17 is initially covered comprehensively with a coating of gold as a cathode material 26. A silver coating deposited there upon as anode material 25 features a plurality of interruptions. The interruptions form in their sum a second surface component 29 in which the anode material 25 is accessible from the outside through the cathode material 26.

In the embodiment shown in FIG. 9 the anode material 26 is deposited on the second surface component 29 not in a comprehensive manner but as a plurality of individual particles. This does not change anything in the effectiveness according to the invention of the coating.

As explained above, the silver is an anode material 25 for the purposes of the invention and the gold is a cathode material 26. Together with the body electrolyte in the vicinity of the implant body 30 the coating 23 forms a plurality of local galvanic elements. Since the gold as cathode material 26 protrudes relative to the anode material 25, the silver ions can move at a small distance to the silver coating also in the direction of the cathode material 26.

In the case of the tooth implant the antimicrobial coating 23 has the particular function to act against microorganisms at the transition between the implant body 30 and the gum 32 or the jaw bone 31. In the vicinity of the mouth it is generally known that there is a plurality of microorganisms and the risk of an infection in the surroundings of the implant body 30 is high. If by means of the antimicrobial coating 23 the intrusion of microorganisms between the implant body 30 and the gum 32 can be eliminated, unpleasant infections for the patient can be prevented. 

1. An implant that releases silver ions in the human body and provides an antimicrobial effect, comprising: an implant component including a first coating portion forming an anode comprising silver and a second coating portion forming a cathode, wherein the first coating portion and the second coating portions are spatially separated, wherein the cathode comprises a material having an electrochemical voltage sequence higher than silver, and wherein the cathode and the anode are coupled in an electrically conducting manner.
 2. The coated implant of claim 1, wherein the anode comprises pure silver.
 3. The coated implant of claim 1, wherein the anode comprises silver having a purity level of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9%.
 3. The coated implant of claim 1, wherein a standard electrode potential for release of silver ions of the anode is less than about +0.8 V.
 4. The coated implant of claim 1, wherein a standard electrode potential of the cathode is greater than about +0.8 V.
 5. The coated implant of claim 4, wherein the cathode material is gold.
 6. The coated implant of claim 1, wherein a standard electrode potential of the cathode is greater than the standard electrode potential of the anode by at least about 0.3 V, about 0.5 V, or about 0.7 V.
 7. The coated implant of claim 1, wherein the cathode material is embedded in the anode in an island-shaped manner.
 8. The coated implant of claim 1, wherein the first surface component that is occupied by the anode occupies greater than about 50%, about 70%, or about 80% of the surface area of the coating.
 9. The coated implant of claim 1, wherein the first surface component that is occupied by the anode occupies greater than about 50%, about 70%, or about 80% of the coating.
 10. The coated implant of claim 1, wherein the anode and the cathode abut against one another in flush manner.
 11. The coated implant of claim 1, wherein the cathode protrudes relative to the anode. 